A satellite laser ranging system denotes a system for measuring a distance to a satellite using laser, and is configured to fire laser light with a short pulse width at a satellite and calculate the distance to the satellite using the time of departure (start) of the laser light, which is the time at which the laser light is fired, and the time of arrival (stop) of the laser light, which is the time at which the laser light, after being reflected by the satellite, arrives at a receiver.
Generally, when laser light is fired at a satellite, the start time of the fired laser light is measured using a high-speed photodiode.
In order to measure the arrival time of the laser light, a received light detection unit (photodetector) for measuring light received after being reflected by the satellite is used.
Since the intensity of light, that is, laser light, reflected by the satellite, is weak, the photodetector may be implemented using a Compensated Single Photon Avalanche Diode (C-SPAD) capable of detecting even a single photon.
Such a C-SPAD has sensitive photon detection performance and is capable of driving a gate in accordance with a time point at which light reflected by the satellite arrives at a location of measurement, receiving a laser signal reflected by the satellite, and precisely measuring the arrival time of the laser signal, thus exactly calculating the distance to the satellite.
In order to drive a gate signal for the C-SPAD, the arrival time of laser light is predicted using an optoelectric control apparatus included in the satellite laser ranging system. The optoelectric control apparatus generates a gate signal for the C-SPAD at the predicted time point.
The optoelectric control apparatus is configured using a personal computer (PC) and an optoelectric interface card installed in the PC. The arrival time of laser light reflected by the satellite is calculated using the PC, and the results of the calculation are transferred to the optoelectric interface card. The optoelectric interface card then generates a gate signal for the C-SPAD using the results of the calculation.
Since an optoelectric signal is generated using the optoelectric interface card, information about the arrival time of laser light reflected by the satellite is calculated by the central processing unit (CPU) of the computer and is transferred to the optoelectric interface card through a slot formed in the optoelectric interface card. Thereafter an optoelectric control signal is generated by the optoelectric interface card.
External signals and data, such as the start time of the laser light and the arrival time of the laser light, calculated by the satellite laser ranging system, are transferred to the computer through the optoelectric interface card. In contrast, signals and data generated by the CPU of the computer are also transferred in real time through the optoelectric interface card.
The CPU of the computer processes the data transmitted through the optoelectric interface card.
Data processing is performed in real time by the satellite laser ranging system using the high-performance CPU installed in the computer, thus improving convenience. However, an interface card for the transmission of signals and data between the computer and the satellite laser ranging system is required.
With a variation in the performance of the computer, the transfer rate and configuration method of the interface card are varied, and so an Operating System (OS) and development software are varied, thus causing the problem of maintenance required for the operation of a satellite laser ranging system that uses a commercial computer in the field.
A power supply device currently being used in a commercial computer in a satellite laser ranging system that requires high-speed signal processing causes the problem of producing unnecessary noise in the satellite laser ranging system.